Cave link

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Cave-Link-System in use at the giant thing shaft cave

Cave-Link is the name of a system for transmitting data through rocks. It is used in caving and mining .

Measurement data and short messages can be transmitted through several hundred meters of rock using the magnetic field of long and long waves (20 to 140  kHz , i.e. 2 to 15 km wavelength ), greater distances are possible by stringing together several devices. For the transmission, a modulated electric current is fed into the rock via two electrodes that are separated from each other . The earth current and the cable together serve as a magnetic antenna . The aim is to send the largest possible current through the longest possible stretch of rock, for which a low earthing resistance is important. The magnetic field spreads in the surrounding rock and can still be detected by the receiver at a distance of 1000 m. Due to the long wavelength (> 10 km), the transmitting and receiving antennas must also be dimensioned correspondingly large, antenna lengths between 50 and 100 m are typically used, an antenna length that corresponds to at least one tenth of the transmission distance is used as a guide. The antennas must be installed in parallel as far as possible, whereby vertical antennas make sense in pronounced shaft caves .

The maximum data transmission rate of 104 bit / s (corresponds to 13 characters per second) is very low, but Huffman coding is used for data compression . The data is transmitted in blocks of 2 bytes, which are sent to avoid transmission errors until the correct transmission has been confirmed by the recipient. Long distances or atmospheric disturbances can greatly reduce the transmission rate. The system can also be operated via a long wire pair. A routing table is used so that Cave-Link devices can communicate with each other, even if one device can only be reached via another . There is a GSM modem for forwarding the data from the outdoor station , and if there is no network coverage, a radio modem, which forwards the signals to a location with a GSM supply.

The system was developed by members of the Hölloch Research Working Group , who are researching the second largest cave system in Europe. It is used there, but also in the Vetterhöhle or the Grotte de Milandre, among other things for the automatic transmission of sensor data for water levels , water temperature , cave wind , air composition, air pressure or air temperature . Several devices were used during the rescue operation in the giant thing shaft cave in June 2014.

Web links

Commons : Cave-Link  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Christian Ebi: data sheet Cave-Link version 10
  2. ↑ a b c d Cave-Link: How the cave radio works . Bergwacht Bayern, June 12, 2014.
  3. ↑ CaveLink telemetry system , website of the Blaubeuren cave association.
  4. ↑ a b c Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2, 2014. Page 10.
  5. ↑ Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2, 2014. Page 14.
  6. ↑ a b Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2nd, 2014. Page 17.
  7. ↑ Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2, 2014. Page 28.
  8. ↑ Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2, 2014. Page 11.
  9. ↑ Christian Ebi, Felix Ziegler: Instructions for Cave-Link with firmware 1.5x , January 2nd, 2014.
  10. ↑ Joachim Striebel: Data come wirelessly from the cave ( Memento from July 16, 2014 in the Internet Archive ), Südwest Presse , November 21, 2009.
  11. ↑ Measuring / Monitoring ( Memento of July 14, 2014 in the Internet Archive ), cavelink.com, accessed on June 25, 2014.
  12. ↑ Rescuers work at the entrance of the giant thing shaft cave with the cave radio system "Cavelink". In: Focus , June 11, 2014.